Background. The design and interpretation of randomized trials is intimately connected to the use of "placebo." The nature and magnitude of placebo effects, however, is very poorly understood. Specific aims. Using a common cold model, this study will assess two kinds of "placebo effects": 1) the effect of receiving blinded placebo, compared to no treatment, and 2) the effect of receiving open-labeled active treatment (echinacea), compared to blinded active treatment. This study will also assess 3) the effects of receiving a standard physician visit, compared to no visit, and 4) the effects of enhancing that visit with patient-oriented attributes. Finally, we will compare and contrast these "placebo effects" and "physician effects". Research design. A randomized controlled trial using a balanced 2-way treatment structure, with concealed allocation where appropriate. Population. Community-recruited adults with new onset common cold. Primary outcome. Severity days of illness, defined as area under the severity duration curve, with severity measured as total score on an illness-specific quality of life measure. Secondary outcomes. Self-reported: general health-related quality of life, perceived stress, interpersonal support, optimism, and patient satisfaction. Laboratory-measured from nasal wash: IL-8 (inflammatory cytokine), neutrophil counts. Counts and weights of nasal tissues used will serve as measures of nasal mucus production. Power. This proposed trial of 800 enrolled participants (720 projected finishers) will have at least 80% power to detect a 20% difference in severity days between treatment groups. Importance. Although the illness- and treatment-specific results of this experiment will be valuable, the primary importance of this study will be to characterize and compare placebo effects attributable to randomization to pill treatments versus randomization to physician-based clinical-interactions.